Citrus Orchards Research Articles

First detection of resistance to deltamethrin in Spanish populations of the Mediterranean fruit fly, Ceratitis capitata

The control of the Mediterranean fruit fly (Medfly), Ceratitis capitata, in citrus orchards in Spain is mainly based in three insecticides (spinosad, lambda-cyhalothrin and deltamethrin) and the liberation of sterile males. However, Medfly control is compromised by the development of lambda-cyhalothrin resistance and the detection of spinosad-resistant alleles in field populations. We report here, for the first time, resistance to deltamethrin in populations collected in fields under different management strategies, including MagnetMed™ traps coated with this insecticide and/or spinosad and lambda-cyhalothrin used as bait sprays, and even in populations obtained from non-treated fields. Two deltamethrin-resistant strains (BP-delta and Rfg-delta) were generated from the descendants of some of the field populations that showed lower susceptibility to deltamethrin. Both strains showed low susceptibility to MagnetMed™ traps, moderate susceptibility to Ceratipack traps, and lacked cross-resistance to spinosad and lambda cyhalothrin. Our data suggest that deltamethrin resistance was mediated by P450 enzymes, since bioassays with synergists showed that PBO reverted resistance in a field population and the laboratory strains, whereas the effect of DEF and DEM was minor and no mutations were found in the VGSC gene. The inheritance of resistance for both strains was completely recessive, autosomic and did not fit the mortality expected for a recessive character under a monogenic or digenic model. We also found that deltamethrin resistance presented a fitness cost in terms of males’ weight, males’ and females’ longevity and lifetime fecundity, with a more pronounced effect in the BP-strain than in the Rfg-delta strain. Our results highlight the need to implement insecticide resistance management strategies to prevent control failures.

A low-toxicity baiting program precipitates collapse of Argentine ant and ant-associated hemipteran pest populations in commercial citrus

The Argentine ant, Linepithema humile Mayr (Hymenoptera: Formicidae), disrupts biological control agents which induces population outbreaks of honeydew-producing hemipteran pests infesting agroecosystems. A multi-season liquid baiting program was evaluated for control of L. humile and ant-associated hemipteran pests in six commercial citrus orchards in southern California. Ant activity in treated trees fell by 96% within three months of treatment and was, on average, 95% lower in treated plots than untreated plots across the 18-month study period. Ant control resulted in the near elimination of hemipteran pest populations on trees in treated plots. Pre- and post-treatment estimates indicated that hemipteran pest infestation of twigs, flush, and fruit decreased by 97, 84, and 99% one year after treatment, respectively. Furthermore, cumulative infestation frequency was 10 times lower and cumulative colony size was 5 times lower on treated trees than control trees across the final year of study. Examining individual hemipteran pest species, the mean infestation rate by Diaphorina citri Kuwayama (Hemiptera: Liviidae) was 75% lower, Coccus hesperidum L. (Hemiptera: Coccidae) 95% lower, Planococcus citri Risso (Hemiptera: Pseudococcidae) 98% – 100% lower, and Aonidiella aurantii Maskell (Hemiptera: Diaspidae) 70 – 80% lower in treated trees relative to untreated trees. A surge in generalist predator activity and parasitism following ant bait deployment appear to be the driving forces behind the marked decrease in pest infestation observed in treated trees. Results underscore the importance of L. humile control for integrated pest management programs targeting ant-associated hemipteran pests in commercial citrus.

Population Dynamics of Arthropods in New Caledonian Citrus Orchards

Aims: Agroecological infrastructures are central to the preservation of arthropod populations and ecosystem services associated. There is little data on the population dynamics of New Caledonian citrus orchards. Thus, this study focuses on the response of arthropods to four management methods in the orchard: conventional management, inter-row vegetated, row mulching and edge windbreaks.
 Place and Duration of Study: This study was conducted in the village of La Foa in New Caledonia. It took place over three months, from the end of February to the end of May 2022.
 Methodology: To collect the greatest possible diversity of insects, four complementary trapping methods were used: pitfall traps, yellow plates, Malaise traps and sweeping nets. Once collected, the trapped insects are then sorted and identified. The sorting is done with a binocular magnifying glass. Insects are identified using specific determination keys, documentation, or with the help of the Reference Collection of Terrestrial Invertebrates of New Caledonia - Xavier Montrouzier (CXMNC). When identification is not immediately possible, a morphotype number is assigned. For each species and morphospecies, a photograph is taken. Alpha and beta diversity was studied using rarefactions, Shannon index and Generalized Linear Models.
 Results: A positive effect of agroecological infrastructures on insects’ abundance and diversity was recorded. In contrast, low arthropod abundances and diversities were presented in the orchard under conventional management (P < 0.001). Mulching management was the parameter showing the much higher insects’ abundance. Moreover, populations dynamics were generally correlated with the related infrastructures. Thus, windbreaks acted as ecological corridors and the inter-row vegetation as refuge habitats for beneficial insects. 
 Conclusion: These results demonstrate the damage of conventional agriculture on arthropod diversity in New Caledonian orchards. They also show that agroecological infrastructures can bring back insect biodiversity, especially with the mulching management.

Geographic Location, Management Strategy, and Huanglongbing Disease Affect Arbuscular Mycorrhizal Fungal Communities Across U.S. Citrus Orchards

The benefits of arbuscular mycorrhizal fungi (AMF) to agroecosystems have been well recognized. Citrus is a globally grown fruit tree commonly found in association with AMF. Global citrus production is currently under the threat of the pandemic huanglongbing (HLB) disease. Since its introduction in the United States, the disease has devastated the Florida citrus industry and is now at the doorsteps of commercial orchards in California. Here, we tested how the two distinct climatic zones within the continental United States where citrus is mostly grown (California and Florida) influenced AMF community diversity and composition. We also assessed in what capacity low-input organic farming and HLB disease affected the AMF communities colonizing the citrus roots. Root samples were collected from 88 trees across 10 orchards. Orchards were selected based on conventional or organic practices in California and based on HLB symptom severity in Florida. AMF communities were characterized using high-throughput sequencing of the small-subunit ribosomal RNA gene. Taxa names were assigned based on a phylogenetic analysis that comprised a backbone of AMF reference sequences from Mycobank and virtual taxa from the MaarjAM database. AMF were detected in 78% of citrus root samples, with taxa belonging to six genera ( Dominikia, Funneliformis, Glomus, Rhizophagus, Sclerocystis, and Septoglomus) and unknown Glomeraceae genera. Geographical location, management practice, and disease affected AMF community composition. We provide evidence that perennial agroecosystems are composed of generalist and specialist AMF taxa comparable with other ecosystems and identified ubiquitous taxa that could potentially be exploited for agricultural purposes.

Decision support strategy for preventing sunburn: Precise prediction of sunburn occurrence reflecting both biotic and abiotic factors in late-maturing citrus orchards

This study emphasized not only the basic concept that the sunburn of fruit was caused by fruit skin temperature rising above its tolerable threshold but also that the threshold was variable, namely, fruit became more vulnerable to sunburn on its own as the growth period progressed. These main results were derived from two major functions: first, multiple linear regression to estimate the fruit skin temperature utilizing solar radiation and ambient air temperature, and second, nonlinear regression with a sigmoid function, which represents the variability in the fruit skin temperature threshold inducing sunburn. The specific major results are as follows. Both individual and multiple regressions showed that the increase in fruit skin temperature was more affected by solar radiation than by ambient air temperature. Considering the entire period from July to September, sunburn was related to fruit skin temperatures above 46 °C. However, the specific investigation dividing the entire period into 10-day periods indicated that the fruit skin temperature threshold for inducing sunburn decreased over time. In the discriminant analysis for predicting the occurrence of sunburned fruits, the prediction accuracy based on the variable threshold was 81.9%, which was higher than 67.0% based on the fixed threshold of 46 °C. The reference ambient air temperature for the occurrence of sunburn decreased with seasonal progress in the field from higher than 35 °C in early August to 28 °C in mid-September and in the greenhouse from higher than 39 °C to 31.7 °C. The variability of thresholds related to the internal tolerance of fruit for sunburn presented the reason why sunburned fruits could occur or increase despite the weakening of abiotic factors inducing sunburn, such as solar radiation and ambient air temperature, as the season progresses from summer to autumn.

Native Rhizobia Improve Plant Growth, Fix N2, and Reduce Greenhouse Emissions of Sunnhemp More than Commercial Rhizobia Inoculants in Florida Citrus Orchards.

Sunnhemp (Crotalaria juncea L.) is an important legume cover crop used in tree cropping systems, where there is increased interest by growers to identify rhizobia to maximize soil nitrogen (N) inputs. We aimed to isolate and identify native rhizobia and compare their capabilities with non-native rhizobia from commercial inoculants to fix atmospheric dinitrogen (N2), produce and reduce nitrous oxide (N2O), and improve plant growth. Phylogenetic analyses of sequences of the 16S rRNA and recA, atpD, and glnII genes showed native rhizobial strains belonged to Rhizobium tropici and the non-native strain to Bradyrhizobium japonicum. Plant nodulation tests, sequencing of nodC and nifH genes, and the acetylene-dependent ethylene production assay confirmed the capacity of all strains to nodulate sunnhemp and fix N2. Inoculation with native rhizobial strains resulted in significant increases in root and shoot weight and total C and N contents in the shoots, and showed greater N2-fixation rates and lower emissions of N2O compared to the non-native rhizobium. Our results suggest that native rhizobia improve plant growth, fix N2, and reduce greenhouse emissions of sunnhemp more than commercial rhizobia inoculants in Florida citrus orchards.

Influence of Temperature Variability on Survival and Development of Citrus Leaf Miner, Phyllocnistis citrella Stainton (Lepidoptera: Gracilariidae) in Tanzania

Due to limited information on Phyllocnistis citrella’s Biology, study was aimed to examine the effects of different temperature levels on biology of citrus leaf miner under controlled laboratory conditions at the Entomology laboratory of Sokoine University of Agriculture (SUA), Tanzania from December 2011 to September 2012. Leaf samples (1,985 leaf samples) considered to contain larvae in serpentine mines were collected and individually incubated at room temperature. The emerging adults were wet preserved in 70% ethanol while some dry preserved using special micro pins under microscope for future identification. A Monterey LG8920 pheromone trap was set in every 10m2 at SUA citrus orchard to trap adult moths to supplement sample sources. Citrus leaf miners species collected were identified and four different temperature levels (20, 25, 30 and 35°C) were monitored at each developmental stage. Results revealed longer development time (egg to adult) at 200C and shorter at 300C in 28 and 10 days while the total mortality was 26.67% at 200C and 6.67% at 300C respectively. Oviposition period and rate were negatively and positively influenced by temperature (from 9.26 days at 200C to 6.21 days at 300C and 15.2 eggs/ female/ day at 300C and 6.8 eggs/ female/ day at 200C respectively). The overall fecundity was 28.2 eggs/ female at 200C and 57.1 eggs/ female at 300C. High larval mortality rate was recorded compared to the egg stage while no mortality observed at pupa stage. Conclusively, the pest on this temperature range (200C, minimum to 300C, maximum) has high fecundity, low mortality rate and the developmental time was positively correlated with high temperature, therefore considered optimum temperature range for its survival and development. Other researches especially Integrated Pest management are imperative for sound management package as per the pest in Tanzania and beyond.

Contributions to the knowledge of the Cicadellini sharpshooters (Hemiptera: Cicadellidae) associated with citrus orchards in Argentina

Xylella fastidiosa Wells et al. is a xylem-borne bacterium that causes some of the most important plant diseases to woody plants such as citrus, olives, almonds and other cultures. This pathogen is mainly transmitted by sharpshooters, among which the tribe Cicadellini (Cicadellinae) includes the largest number of proven vectors. The correct identification of the vectors, along with biological and phenological information, are necessary to identify the key vectors involved in the spread of the bacterium and, consequently, establish control strategies and evaluate risks at a local or regional scale. However, lack of information on the Cicadellini from Argentina has delayed the implementation of control measures. Based on surveys conducted in the main citrus producing areas along with bibliographic data, this contribution provides the first list of Cicadellini species from Argentina that are potential vectors of X. fastidiosa; an identification key to these sharpshooters is provided. Twelve species were recorded from northeastern citrus groves, while from northwestern orchards, with previous information totally absent, 10 species were recorded. Eight species are shared by all producing regions, and five of them are proven vectors of X. fastidiosa (Bucephalogonia xanthophis (Berg), Dilobopterus costalimai Young, Macugonalia cavifrons (Stål), M. leucomelas (Walker), Sonesimia grossa (Signoret)). This contribution provides 22 new insect-plant relationships, information on their natural enemies, the geographic distribution of all species is broadened and the female genitalia of three proven vectors are described for the first time.

Assessment of crop evapotranspiration and deep percolation in a commercial irrigated citrus orchard under semi-arid climate: Combined Eddy-Covariance measurement and soil water balance-based approach

An accurate estimate of crop coefficient (Kc) values at different development stages (Kcini, Kcmid, and Kcend) is crucial for assessing crop water requirements in semi-arid regions. The objectives of this study were first to quantify the reference evapotranspiration (ETo) and to calculate the actual evapotranspiration (ETa) over citrus in a semi-arid climate under drip irrigation. For this purpose, a site of a citrus orchard in Souss-Massa, planted with the Esbal variety of clementine, was equipped with an Eddy-Covariance (EC) system, and sensors to measure radiation, soil heat flux, and micrometeorological forcing data, during 2020 and 2021 seasons. Also, the soil moisture content at various soil depths in the root zone near the EC tower was monitored. The energy balance closure (EBC) approach was adopted for flux assessment to ensure a quality check for the EC measurements. The obtained EBCs were about 82% and 79% for the daily measurements in 2020 and 2021, respectively, which can be considered acceptable considering the nature of the citrus orchard (relatively tall and sparse). Second, the study aimed to estimate actual Kc act values for citrus under the same irrigation strategy. The derived values were compared to different recommended Kc values in the literature. In the third stage, this work aimed to offer an alternative plan to sustainable irrigation management by elaborating an irrigation schedule for citrus crops in the region using the FAO-56 simple approach to avoid water stress and deep percolation (i.e., Ks = 1 and DP = 0). Eventually, an irrigation schedule was drawn following the crop’s phenological stages. The seasonal mean citrus evapotranspiration (ETa) values are 1.68, 3.02, and 1.86 mm/day for the initial, mid, and end-season. The seasonal actual Kc act values were 0.64, 0.58, and 0.64 for Kcini, Kcmid, and Kcend, respectively. Additionally, the application of the water balance equation revealed that a large quantity of water is lost through deep percolation (52% of total water supplied). The study focuses on Citrus trees being a strategic crop with important socio-economic values in the Souss-Massa region. Thus, the results should support both scientists and farmers in planning and strategy development.

Fruit Characteristics of Citrus Trees Grown under Different Soil Cu Levels.

The effects of the increased soil copper (Cu) on fruit quality due to the overuse of Cu agents have been a hot social issue. Seven representative citrus orchards in Guangxi province, China, were investigated to explore the fruit quality characteristics under different soil Cu levels and the relationship between soil-tree Cu and fruit quality. These results showed that pericarp color a value, titratable acid (TA), and vitamin C (Vc) were higher by 90.0, 166.6, and 22.4% in high Cu orchards and by 50.5, 204.2, and 55.3% in excess Cu orchards, compared with optimum Cu orchards. However, the ratio of total soluble solids (TSS)/TA was lower by 68.7% in high Cu orchards and by 61.6% in excess Cu orchards. With the increase of soil Cu concentrations, pericarp color a value and Vc were improved, TA with a trend of rising first then falling, and TSS/TA with a trend of falling first then rising were recorded. As fruit Cu increased, pericarp color a value and TSS reduced and as leaf Cu increased, TSS/TA decreased while Vc was improved. Moreover, a rise in soil Cu enhanced leaf Cu accumulation, and a rise in leaf Cu improved fruit Cu accumulation. Fruit Cu accumulation reduced fruit quality by direct effects, leaf Cu improved fruit quality by direct and indirect effects. Soil Cu affected fruit quality by indirect effects by regulating leaf Cu and fruit Cu. Therefore, reasonable regulation and control of soil Cu concentrations can effectively increase pericarp color, sugar, and acid accumulation in citrus fruit.

Being prepared for huanglongbing disease of citrus: a simulation exercise workshop for contingency planning held in Valencia, Spain

AbstractContingency plans aim to ensure a rapid and effective response to an outbreak of a pest likely which is to have a major impact. Huanglongbing is a devastating disease of citrus not yet present in the European and Mediterranean Plant Protection Organization (EPPO) region. A simulation exercise workshop for contingency planning was held in Valencia, Spain over 3 days in October 2021 as part of the PRE‐HLB project funded by the European Union Horizon 2020 programme. In total, 49 experts from the EPPO region attended the workshop. Participants represented a range of stakeholders from citrus cooperatives, grower associations, nursery workers, citrus exporters, landscapers and gardeners, scientists, Regional Plant Health Authorities, National Plant Protection Organizations and the European Commission. Participants were split into five groups and each group acted as an outbreak management team for a scenario based on a finding of a quarantine pest. The scenario followed the first (fictitious) finding of Diaphorina citri (the insect vector of ‘Candidatus Liberibacter asiaticus’, a causal agent of huanglongbing) at a citrus orchard in Spain. As the scenario developed over a month time scale, each team had to organize themselves to manage a number of issues designed to mimic the development of an outbreak of huanglongbing of citrus over the course of the exercise. The groups acknowledged the usefulness of the Spanish contingency plans for huanglongbing and its vectors, the EPPO Standards, and the risk‐based surveillance design tool RiBESS+.

Mitigation of nutrient runoff loss using reduced nitrogen application and green manure planting in citrus orchard in Hubei, China

Mitigation of nutrient runoff loss using reduced nitrogen application and green manure planting in citrus orchard in Hubei, China

Preharvest Foliar Application of Si–Ca-Based Biostimulant Affects Postharvest Quality and Shelf-Life of Clementine Mandarin (Citrus clementina Hort. Ex Tan)

Citriculture and the postharvest industry are in the quest for biostimulants that favour fruit quality and extend shelf-life. Recently, Si has emerged as a biostimulant and its impact on fruit quality and postharvest shelf-life needs to be elucidated. The experiment is conducted for two consecutive years (2019 and 2020) in a commercial citrus orchard. In the present study, a Si–Ca-based product (Gravital® Force SC, AGROLOGY SA, Sindos, Greece) is foliar sprayed upon clementine mandarin (Citrus clementina Hort. Ex Tan cv. SRA 63) trees from August to November, while unsprayed trees are kept as controls. At commercial maturity, both sprayed and unsprayed fruits are harvested and stored for thirty (30) days at 5 °C with 90–95% relative humidity. Afterwards, they are kept at shelf temperature (20 °C) for six (6) days (shelf-life). At different intervals [at harvest, after cold storage (30 d at 5 °C), at the third day of shelf-life (30 d at 5 °C plus 3 d at 20 °C) and sixth day of shelf-life (30 d at 5 °C plus 6 d at 20 °C)], fruits are sampled and analysed for their qualitative characteristics. According to the results, the preharvest foliar application of the Si–Ca-based product delayed fruit maturation, increased peel firmness, total soluble content, total acidity, ascorbic acid, total phenols and antioxidant capacity, and reduced fruit decay during shelf storage. Results suggest that the preharvest foliar spray of Si–Ca products is able to maintain the postharvest quality of mid-ripening mandarin fruit.

Integrated Pest Management Strategies for Asian Citrus Psyllid Diaphorina citri Kuwayama (Hemiptera: Psyllidae) and Huanglongbing in Citrus for Sarawak, East Malaysia, Borneo.

Simple SummaryThe severe Asian form of huanglongbing is the most serious disease of citrus in Malaysia. It is caused by a phloem-limited bacterium ‘Candidatus Liberibacter asiaticus’ and transmitted by the Asian citrus psyllid, Diaphorina citri Kuwayama. Minimising the devastating impacts of the disease requires effective integrated pest management (IPM) programs to limit detrimental environmental and health consequences of over-reliance on synthetic pesticides. Key components of such programs include grower awareness, planting of pathogen-free trees, monitoring psyllid and disease incidence, removal of diseased trees, and judicious use of insecticides, mineral oils, and natural enemies to suppress incidence of the psyllid. Significant progress has been made towards implementing the programs.The Asian citrus psyllid (ACP), Diaphorina citri Kuwayama, transmits ‘Candidatus Liberibacter asiaticus’ (CLas), a phloem-limited bacterium associated with the severe Asian form of huanglongbing (HLB), and the most destructive disease of citrus. The pathogen and the psyllid, both of South Asian origin, are now widespread in citrus regions of Asia and the Americas. There is no cure for the disease. Application of synthetic pesticides, in some instances more frequently than fortnightly, to minimise incidence of ACP in citrus orchards, has not prevented inevitable impacts of the disease in regions of Asia where CLas is present. Despite the inevitable spread of the disease, significant progress has been made in Sarawak since the mid-1990s towards effectively implementing integrated pest management (IPM) programs for stemming the impact of the disease and detrimental consequences of over-reliance on synthetic pesticides. Growers are encouraged to plant pathogen-free trees, remove diseased trees, monitor incidence of the psyllid, and to use pesticides judiciously to reduce their detrimental impacts on natural enemies. Knowledge has been enhanced through research on seasonal incidence of the psyllid, use of mineral oils, development of protocols and iodine–starch test kits for detecting infected trees, PCR for confirming the presence of CLas in symptomatic leaves, methods for monitoring incidence the psyllid, and training extension staff and growers. However, major impediments to increasing the average longevity of trees beyond <5 years in poorly managed orchards, based on marcotting (air layering), and >12 years in well-managed orchards, based on pathogen-free trees, still need to be addressed. These include grower knowledge, marcotting, aggressive marketing of synthetic pesticides, high prices of mineral oils, spray application procedures, and better reliance on natural enemies of the psyllid.

Citrus Red Mite (Panonychus citri): A Pest of Citrus Crops

Panonychus citri is a phytophagous mite of economic importance in open citrus orchards and a major pest in Citrus Under Protective Screen (CUPS), a new undercover production system tested in Florida. Immatures and adults feed on citrus leaves, fruits, and green twigs resulting in mesophyll collapse, shoot dieback, and fruit drop. In Florida, P. citri occurs throughout the year but is most abundant in spring or early summer and autumn or early winter. Although chemical sprays like Abamectin or Fenbutatin oxide provide some control of P. citri, resistance has been reported in different regions of the world. Several predatory insects and mites have been shown to attack the mite and could be potential natural enemies to use in biological control programs.

A soil sampling method to estimate the population density of Tylenchulus semipenetrans cobb, 1913 in infested citrus orchards of the Fars province in Southern Iran

A soil sampling method to estimate the population density of Tylenchulus semipenetrans cobb, 1913 in infested citrus orchards of the Fars province in Southern Iran

Estimating crop coefficients and actual evapotranspiration in citrus orchards with sporadic cover weeds based on ground and remote sensing data

Accurate estimations of actual crop evapotranspiration are of utmost importance to evaluate crop water requirements and to optimize water use efficiency. At this aim, coupling simple agro-hydrological models, such as the well-known FAO-56 model, with remote observations of the land surface could represent an easy-to-use tool to identify biophysical parameters of vegetation, such as the crop coefficient Kc under the actual field conditions and to estimate actual crop evapotranspiration. This paper intends, therefore, to propose an operational procedure to evaluate the spatio-temporal variability of Kc in a citrus orchard characterized by the sporadic presence of ground weeds, based on micro-meteorological measurements collected on-ground and vegetation indices (VIs) retrieved by the Sentinel-2 sensors. A non-linear Kc(VIs) relationship was identified after assuming that the sum of two VIs, such as the normalized difference vegetation index, NDVI, and the normalized difference water index, NDWI, is suitable to represent the spatio-temporal dynamics of the investigated environment, characterized by sparse vegetation and the sporadic presence of spontaneous but transpiring soil weeds, typical of winter seasons and/or periods following events wetting the soil surface. The Kc values obtained in each cell of the Sentinel-2 grid (10 m) were then used as input of the spatially distributed FAO-56 model to estimate the variability of actual evapotranspiration (ETa) and the other terms of water balance. The performance of the proposed procedure was finally evaluated by comparing the estimated average soil water content and actual crop evapotranspiration with the corresponding ones measured on-ground. The application of the FAO-56 model indicated that the estimated ETa were characterized by root-mean-square-error, RMSE, and mean bias-error, MBE, of 0.48 and -0.13 mm d−1 respectively, while the estimated soil water contents, SWC, were characterized by RMSE equal to 0.01 cm3 cm−3 and the absence of bias, then confirming that the suggested procedure can produce highly accurate results in terms of dynamics of soil water content and actual crop evapotranspiration under the investigated field conditions.

Arthropod Community Responses Reveal Potential Predators and Prey of Entomopathogenic Nematodes in a Citrus Orchard

The contributions of soil arthropods to entomopathogenic nematode (EPN) food webs are mainly studied in artificial conditions. We investigated changes in arthropod communities in a citrus orchard following soil inundation with Steinernema feltiae or Heterorhabditis bacteriophora. We hypothesized that arthropod taxa, which decline or increase in response to EPN augmentation, represent potential prey or predators of EPN, respectively. Soil was sampled periodically after nematodes were applied, DNA was extracted from organisms recovered by sucrose centrifugation, libraries were prepared, and the ITS2 and CO1 genes were sequenced using Illumina protocol. Species from 107 microarthropod (mites and collembola) families and 121 insect families were identified. Amplicon sequence variant (ASV) reads for H. bacteriophora were less than 10% of those for S. feltiae three days after inundation, whereas microarthropod ASVs were double in plots with H. bacteriophora compared to those with S. feltiae. Significantly fewer microarthropod and insect reads in S. feltiae compared to untreated plots suggest the possibility that S. feltiae preyed on mites and Collembola in addition to insects. The responses over time of the individual microarthropod species (MOTU) suggest that regulation (up or down) of these EPN resulted from a cumulative response by many species, rather than by a few key species.

Yeast mediates the interspecific interaction between introduced Bactrocera dorsalis and indigenous Bactrocera minax.

Host plant-microbe associations mediate interspecific interactions amongst herbivorous insects. However, this theory has rarely been ecologically verified in tephritid fruit flies. Research on this subject can not only help predict tephritid species invasion and occurrence patterns, but also develop potential novel lures for the control of the tephritid fruit fly pests. Recently, we observed mixed infestation of Bactrocera minax and Bactrocera dorsalis larvae in citrus orchards, which prompted us to explore the underlying mechanism. Following oviposition by B. minax, the yeast Pichia kluyveri translocated to and proliferated inside the citrus fruit. The level of d-limonene released from citrus fruits containing P. kluyveri was 27 times higher than that released from healthy fruits. Mature B. dorsalis females were attracted to d-limonene and oviposited into fruits previously infested by B. minax. Furthermore, the interspecific interaction between B. dorsalis and B. minax within the same fruit significantly decreased the number of surviving larvae and pupal weight in B. dorsalis, but its effect on B. minax was weaker. In the studied interspecific interaction, B. minax occupies the dominant position, implying ecological significance for this species in terms of consolidating its own niche and inhibiting the invasion of exotic species. To our best knowledge, this is the first report from both ecological and physiological perspectives on a symbiotic yeast mediating the interaction between B. minax and B. dorsalis through altering fruit volatiles. © 2022 Society of Chemical Industry.

Realizing certainty in an uncertain future climate: modeling suitable areas for conserving wild Citrus species under different change scenarios in India.

Citrus is an important horticultural crop of India and is often prone to diseases, particularly under increased temperature scenarios. For developing disease-resistant Citrus varieties, conservation of wild relatives is extremely important. However, our knowledge on temperature tolerance of these wild relatives of Citrus to varied climate change scenarios is extremely limited. Therefore, we determined the climatic niche of six wild relatives of cultivated Citrus species (C. indica Tanaka, C. karna Rafin., C. latipes (Swingle) Tanaka, C. macroptera Montrouz., C. medica L., and C. sinensis (L.) Osbeck.) and identified the geographical areas in India that would remain climatically stable in future through ecological niche modeling (ENM). Raster data on 19 bioclimatic variables with a resolution of 0.04° were used to generate niche models for each Citrus species that delineated their potential distribution areas. Future species distribution predictions for the year 2050 were made using the climate change scenarios from the most appropriate climate models, i.e., IPSL-CM5A-LR and NIMR-HADGEM2-AO with four Representative Concentration Pathways (RCPs). Ensemble of current and future projections was used to identify climatically stable areas for each species. Precipitation-related bioclimatic variables were the key climatic determinants for the modeled distribution pattern. The consensus of current and future projections suggests that most areas with stable climates for the species in the future would be available in the northeastern states of Arunachal Pradesh, Meghalaya, Mizoram, and Tripura. Efforts for in situ conservation and establishment of germplasm banks and citrus orchards may be encouraged in these identified areas.